In line with the technical trend of higher-density magnetic disks (also called hard disks), medium structures of a discrete track type in which magnetic regions generating magnetic signals are partitioned by nonmagnetic sections have been suggested. Further, bit-patterned media in which data track sections are partitioned not only by circumferential grooves but also by every data bit have been suggested. Also, there has been a suggested technique of forming and processing dots by taking advantage of the self-assembling properties of a block copolymer. However, controlling dots to be aligned in an orderly fashion is regarded as difficult particularly in a wide area. To solve this problem, a technique using guide dots and a technique of forming respective dot patterns by electron beam lithography have been suggested.
Where a self-assembled material is used, each bit pattern is formed in the following manner. A diblock copolymer solution with self-assembling capability is applied in guide patterns that are formed beforehand on a substrate surface through an electron beam lithography process or are formed in a later step. Annealing is then performed, to cause microlayer isolation between a first component aggregated into dots and a second component covering the dots. In this manner, the respective dots are self-assembled, or ideally, are aligned in a hexagonal fashion. After that, by using the difference in etching characteristics (the etching rate difference) between the first component and the second component, substrate processing is performed, with one of the first component and the second component being used as a mask. In this manner, the respective bit patterns can be formed. Here, to control the alignments of the self-assembled material, position control regions for controlling the alignments of dots and free diffusion regions for allowing the dots to be aligned in a self-assembled manner should preferably be provided on the substrate.
The range in which a self-assembled material is aligned in a self-assembled manner as described above can be restricted to a certain range by providing guide grooves or a position control region. However, the circumferential width of a guide varies with radial position in a magnetic disk. Therefore, the number of dots of a self-assembled material that can be provided in a circumferential width of a guide varies with radius. In view of this, it is inevitable that guide patterns with different widths in a circumferential direction include some portions in which the alignments of the self-assembled material are not uniform. As a result, preamble signals and burst signals generated based on the dots of the self-assembled material arranged in such an irregular fashion become uneven in terms of timing, and it becomes difficult to obtain synchronization signals in preamble sections and detect phase differences in burst sections of a phase difference type.